1. Field of the Invention
The present invention relates to an electro-optical device for the display of dark symbols composed of separately selectable display segments against a bright background, and to means of addressing this kind of display device.
2. Description of the Prior Art
A display device is known from the German Patent Disclosure DT-OS No. 24 50 698 where the area of each electrode element of the front electrode has the same shape and area as the display segments themselves. The liquid crystalline medium between the front and the rear electrode elements corresponding to a particular symbol can be optically activated by applying electrical signals to these electrodes. The ambient light falling upon this region is scattered so that an observer can read the selected symbol. Display cells of this type are designed to use the Dynamic Scattering Effect. Such displays are not always suitable when electro-optical media are employed that operate upon other electro-optical effects. For example a cholesteric guest-host electro-optic substance would display bright symbols against a dark background in such a display cell. This is generally not desirable because optimum readability of a displayed symbol is obtained when it appears as a dark area against a bright background, like the printed letters of a newspaper. Display devices employing cholesteric guest-host substances, on the other hand, are especially attractive because they require lower operating voltages and have a lower power consumption than dynamic scattering displays and, compared to twisted nematic displays, they don't need polarizers or special surface treatments on the inner walls of the cell.